In general, a torque converter used in an automobile with an AT (automatic transmission) has a cover and is filled with operating fluid (oil) with a pump rotating together with the cover, a turbine arranged oppositely to the pump, and a stator connected to a one-way clutch adapted to transmit rotation of pump to the turbine via the fluid while increasing the transmitting torque. Accordingly, the driving power of an engine can be amplified via the fluid and transmitted to the transmission and wheels.
A lock-up clutch apparatus arranged within the cover of torque converter is intended to reduce the loss of torque transmission as compared with the torque transmission via fluid by directly connecting the cover of torque converter and the turbine at an appropriate timing. Japanese Patent Document JP 2011-185382 A discloses a multiple disc type lock-up clutch apparatus arranged within a cover of a torque converter. The lock-up clutch comprises a clutch piston operable between an operated position and a non-operated position and is able to urge driving clutch discs arranged on the cover-side in the operated position, a hub gear for holding driven clutch discs arranged opposed to the driving clutch discs and able to transmit the power to the hub gear with being press-contacted with driving clutch discs when the clutch piston is in the operated position, and a torque transmitting member connected to the hub gear via damper springs and rotatable together with the hub gear to transmit the engine torque to the turbine of torque converter.